We’re trying to write a unit test engine for Xcode. (We know there’s an open source one, but it has some issues. We might try to contribute to that project, but for now we’re starting with writing our own engine for our own private use.)
A problem that we’re running into (that the published one has as well), is that you can’t specify any custom configuration in the .arcunit file (e.g. the name of the Xcode scheme you need to use to run unit tests).
It would be great if ArcanistUnitTestEngine had similar hooks that ArcanistLinter does to get configuration, i.e. getEngineConfigurationOptions and setEngineConfigurationValue functions. I wrote a pretty trivial patch to do just that at https://secure.phabricator.com/D18815 .